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Old Oct 03, 2014, 12:52 PM
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United States, IN, South Bend
Joined Apr 2013
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muffler pointing

Will someone save me some experimentation time and tell me what the most likely direction point the muffler to NOT get fuel all over my plane with an OS surpass engine?
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Old Oct 03, 2014, 02:00 PM
WCB
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NC
Joined Aug 2005
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I've found with glow engines that most of the time if you point it down the oil goes all over the bottom surfaces. Pointed up it goes all over the top. I've used the little exhaust extensions and they help some, but not much.
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Old Oct 03, 2014, 05:10 PM
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Joined Oct 2004
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I've seen guys point the muffler straight up to try and reduce oiling of the plane.

Looks really dumb and I doubt that it helps that much.
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Old Oct 03, 2014, 07:25 PM
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United States, NY, Syracuse
Joined Oct 2008
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All you can do is try to point it away from as much of the plane as possible. Wherever the exhaust goes there will be oil all over the plane. It's just part of operating glow planes.
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Old Oct 04, 2014, 08:55 AM
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Joined Jan 2012
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I point up on a low wing, and down on a high wing. An extension helps to keep the goo off the wing, but the tail still gets it. I try to get it down a bit so puddles of fuel don't collect when filling the tank etc. A low wing plane plane make this harder, I just point the nose up after filling, while making sure the piston is at TDC while filling. A long tuned pipe, or largish diameter tubing extension past the tail may help if you really care. It could attach to the muffler, or even just a pipe header if noise will not be an issue. A small restriction at the back of the tubing can assist in back pressure for the tank, and even make somewhat of an adjustable pipe.
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Old Oct 04, 2014, 09:42 AM
Complete RC Idiot Savant
The Netherlands
Joined Nov 2009
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If your engine is tight at the front bearing, what you can do is use an exhaust pipe all the way to behind the tail. Either inside or outside the fuselage.

I have seen that done several times without even the slightest downside, except for maybe a bit of power loss....
On 2 strokes usually you can use silicon or Tygon tubing without any problems.
To avoid backpressure issues, you can opt to use a tubing with twice the diameter of the tail pipe, and just stick the tailpipe in with an airgap. The eductor effect will draw in fresh air, reduce the tube temperature and eliminate backpressure...

Then the only oil spray remaining is a bit of sputtering from the carb at part-load, and that can be eliminated with the use of a "velocity-stack" of some sort.

But if your engine once has developed "the nose bleed", everything you do is in vain...

Brgds, Bert
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Old Oct 06, 2014, 08:37 AM
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Also, you do realize that your crankcase breather is also spitting out oil?
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Old Oct 06, 2014, 11:23 AM
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United States, TX, Weatherford
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Our little IC engines use the "Loss Lubrication" method, that is what is not consumed by the engine is ported over board by the exhaust system. Most fuels use some or all Castor oil as the lubricant. It is generally not consumed by combustion as its burn temperature is higher than that of combustion. That is not a bad thing, since the oil also carries away the heat generated by the combustion, a good thing.

If you have a four cycle engine and you point the exhaust straight up as I have seen here and there trying to avoid the oil residue. that is not a wise configuration. The four cycle engine has quite a big pulse on firing and when you extend the moment of the muffler up and away, the impulse is felt by the muffler. It will cause engine rock in the mounts and lead to lose bolts on the engine mount to the aircraft and engine to engine mount also. It will also, if the bolts are tight and have lock-tite on them, can lead to fire walls coming lose. Pointing the muffler aft reduces this phenomena a bit, a least reduces the overall moment at the tip of the muffler.

I have read where some folks have worn the threads out in the engine head from this configuration. The short pipe from the head to the muffler is harder material than the aluminum head, so the threads, if not tight, will wear in the head. Another reason not to point the muffler straight up.

As said previously, oil clean up comes with the use of IC engines. If it bothers you that much, go to electrics.
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Old Oct 06, 2014, 11:31 AM
Traranisaurus TX
United States, GA, Cartersville
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Quote:
Originally Posted by tacx View Post
Also, you do realize that your crankcase breather is also spitting out oil?
True, though you can negate this to some extent by attaching a piece of fuel tubing, to direct the oil away from the air frame as much as possible. This is a good idea, especially with cowled engines.
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Old Oct 06, 2014, 12:03 PM
Complete RC Idiot Savant
The Netherlands
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Quote:
Originally Posted by Chip01 View Post
Our little IC engines use the "Loss Lubrication" method, that is what is not consumed by the engine is ported over board by the exhaust system. Most fuels use some or all Castor oil as the lubricant. It is generally not consumed by combustion as its burn temperature is higher than that of combustion. That is not a bad thing, since the oil also carries away the heat generated by the combustion, a good thing.

If you have a four cycle engine and you point the exhaust straight up as I have seen here and there trying to avoid the oil residue. that is not a wise configuration. The four cycle engine has quite a big pulse on firing and when you extend the moment of the muffler up and away, the impulse is felt by the muffler. It will cause engine rock in the mounts and lead to lose bolts on the engine mount to the aircraft and engine to engine mount also. It will also, if the bolts are tight and have lock-tite on them, can lead to fire walls coming lose. Pointing the muffler aft reduces this phenomena a bit, a least reduces the overall moment at the tip of the muffler.

I have read where some folks have worn the threads out in the engine head from this configuration. The short pipe from the head to the muffler is harder material than the aluminum head, so the threads, if not tight, will wear in the head. Another reason not to point the muffler straight up.

As said previously, oil clean up comes with the use of IC engines. If it bothers you that much, go to electrics.
I know I should keep silent, but I can't from so much nonsense.

Oil does NOT, repeat NOT cool... it carries away at best 2 or 3% of the total generated heat. There simply is no more heat-absorbing capacity (specific heat times temperature rise times massflow) in the oil as supplied in ratio with the fuel.

Then the pulses from an exhaust that is pointed upwards, rattling loose engine mounting bolts or firewall.... Serious????

Are you saying that the reaction forces of the exhaustgasses (gasses that have lost virtually all of their kinetic energy to the piston, in the preceding powerstroke) flowing through the exhaust, are larger than the torque pulses driving the prop?
Or even large enough, to overstretch the engine mounting bolts, obviously strained to their limits by the normal power pulses???
If that were true, then remove the prop and point the exhaust backwards, because you'd get more propulsion from the exhaust than from the prop....

The stripped threads in the exhaust connection in the head, yes, that is a possibility, but that has nothing to do with the pulses of exhaust gas, but everything with the engine shaking sideways due to the torque pulses, and the centre of that rotation is the crankshaft.
Pointing the exhaust away, increases the distance between the mass of the muffler and the axis of rotation, and in the formula for inertia moment, that distance acts to the power of three.... THAT is why you can strip those threads, NOT because the impuls from the gas flow...

Brgds, Bert
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Old Oct 06, 2014, 02:51 PM
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I think Bert has answered it quite well. I agree with him on it.
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Old Oct 08, 2014, 05:18 PM
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Originally Posted by Brutus1967 View Post
Oil does NOT, repeat NOT cool...
Not trying to start anything, but if your statement is true, then every book on engines ever written is wrong. Oil does indeed cool every IC engine. Cooling is one of oils main duties in an engine, aside from preventing wear, minimizing friction, cleaning away impurities. Argue against this all you like, and I'll stand by my FAA A&P license and 15 years as an automotive mechanic that it does indeed cool. All the rest I agree with.
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Old Oct 08, 2014, 05:42 PM
Complete RC Idiot Savant
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And I sir, I stand my 25 years as a marine chief engineer...

In any engine with an oil sump or circulation, YES.... oil does cool! Not really much, usually only approx 10% of the amount of heat cooled away via the cooling water (in a liquid cooled engine) or the fins (air cooled engine) but yes, it does cool, and the cooling is significant to the functioning of the engine.

But on any engine with mixture lubrication, oil does NOT cool, or at least, only negligable....
How would oil cooling be done, if an engine running a 1:50 mix, gets 20 cc of oil for every litre of fuel, and that litre of fuel delivers roughly 35 MJ of heat. Roughly 20% of that is converted into labour, the rest, 28 MJ needs to be cooled away, one way or another. approx 14 MJ of that heat leaves the exhaust with the gasses, so there is still 14 MJ to be cooled away.
How is 20 cc of oil, with a specific heat of approx 1.2 KJ per litre per degree (thus, at say, a delta T of 100 degrees, for the 20 cc it can absorb something like 2.4 KJ) going to cool that engine? 14 MJ of heat "on offer" against 2.4 KJ of maximum absorption capacity??? That is like a single volunteer helping in cleaning up the mexican gulf oil spill and claiming his roll of toilet paper made the difference...

Glow engines have ten times as much oil and half the heat supplied, so there you would get something like 7 MJ against 24 KJ.... still a very uneven battle....

there simply is not enough oil passing the engine for the oil to have ANY cooling effect....

Still not convinced? (you said after all: "Argue all you want"):
For example a fourstroke engine with a sump, consuming 1 litre staight gas per hour, has half a litre of oil in the sump, and that amount of oil circulates at least once per minute through the system, but probably much faster. Which comes down to 30 litres per hour at least.
That 30 litres per hour, absorb 10% of the total cooled amount.

Now a two stroke, consuming that same 1 litre per hour will only receive 20 cc of oil per hour.... Still thinking that amount of oil has significant cooling function?

Like I said, I stand by my 25 years as marine engineer. As such, I learned to deal with numbers and facts, flowrates, energy flows, and such, rather than how to adjust valves or change filters.... That is not meant condescending, but my engineers training has been entirely different than yours, more directed at in-depth engineering.

Any book that writes two strokes (not the big naval diesels with an oil sump, but the "gardenvariety" running on 2-stroke mix) that states that oil cools, is indeed written wrong. VERY wrong.

But I know of no such book, as all books stating that oil cools, refer to engines with an oil sump and forced circulation lubrication....

I can even make it worse: too much oil in a two stroke mix generates heat....

Some tests have clearly indicated that for example a 4-stroke glow running on 20% oil mix, even when properly adjusted for the mixture, runs noticeably hotter
than one running on 10% oil, and also my Zenoahs, working in helicopters, run cooler on 1:40 than they do on 1:25. And that is a fact, not a fairytale.
Brgds, Bert
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